I sat with an American friend one time and discussed something similar. She wrote down a list of words that rhymed with "Ferrari" as an experiment - it included "Marry" and "Mary" among others, which do not rhyme in most English pronunciations (but do in Scotland, interestingly).
That plus the fact that US intonation is not necessarily related to the sense of the sentence being spoken - in many cases, particularly with young people and even more so with Californian young people, every sentence has the same cadence and intonation, regardless of its meaning. To English ears, anyway.
The funny thing is, the moment I land on US soil I start slipping into a (doubtless poor) American voice, quite embarrassingly sometimes. I'm just a Yankophile.
:)